12 research outputs found
An upper limit on the mass of the circumplanetary disk for DH Tau b
DH Tau is a young (1 Myr) classical T Tauri star. It is one of the few
young PMS stars known to be associated with a planetary mass companion, DH Tau
b, orbiting at large separation and detected by direct imaging. DH Tau b is
thought to be accreting based on copious H emission and exhibits
variable Paschen Beta emission. NOEMA observations at 230 GHz allow us to place
constraints on the disk dust mass for both DH Tau b and the primary in a regime
where the disks will appear optically thin. We estimate a disk dust mass for
the primary, DH Tau A of , which gives a disk-to-star
mass ratio of 0.014 (assuming the usual Gas-to-Dust mass ratio of 100 in the
disk). We find a conservative disk dust mass upper limit of 0.42
for DH Tau b, assuming that the disk temperature is dominated by irradiation
from DH Tau b itself. Given the environment of the circumplanetary disk,
variable illumination from the primary or the equilibrium temperature of the
surrounding cloud would lead to even lower disk mass estimates. A MCFOST
radiative transfer model including heating of the circumplanetary disk by DH
Tau b and DH Tau A suggests that a mass averaged disk temperature of 22 K is
more realistic, resulting in a dust disk mass upper limit of 0.09
for DH Tau b. We place DH Tau b in context with similar objects and discuss the
consequences for planet formation models.Comment: accepted for publication in A
The ALMA Early Science View of FUor/EXor objects. IV. Misaligned Outflows in the Complex Star-forming Environment of V1647 Ori and McNeil's Nebula
We present Atacama Large Millimeter/sub-millimeter Array (ALMA) observations
of the star-forming environment surrounding V1647 Ori, an outbursting FUor/EXor
pre-MS star. Dust continuum and the (J = 2 - 1) CO, CO, CO
molecular emission lines were observed to characterize the V1647 Ori
circumstellar disc and any large scale molecular features present. We detect
continuum emission from the circumstellar disc and determine a radius r = 40
au, inclination i = 17 and total disc mass of
M of ~0.1 M. We do not identify any disc structures
associated with nearby companions, massive planets or fragmentation. The
molecular cloud environment surrounding V1647 Ori is both structured and
complex. We confirm the presence of an excavated cavity north of V1647 Ori and
have identified dense material at the base of the optical reflection nebula
(McNeil's Nebula) that is actively shaping its surrounding environment. Two
distinct outflows have been detected with dynamical ages of ~11,700 and 17,200
years. These outflows are misaligned suggesting disc precession over ~5500
years as a result of anisotropic accretion events is responsible. The
collimated outflows exhibit velocities of ~2 km s, similar in velocity
to that of other FUor objects presented in this series but significantly slower
than previous observations and model predictions. The V1647 Ori system is
seemingly connected by an "arm" of material to a large unresolved structure
located ~20 to the west. The complex environment surrounding V1647 Ori
suggests it is in the early stages of star formation which may relate to its
classification as both an FUor and EXor type object.Comment: 18 pages, 14 figures, 4 tables; accepted for publication in MNRA
Evolution of protoplanetary disks from their taxonomy in scattered light: Group I vs. Group II
High-resolution imaging reveals a large morphological variety of
protoplanetary disks. To date, no constraints on their global evolution have
been found from this census. An evolutionary classification of disks was
proposed based on their IR spectral energy distribution, with the Group I
sources showing a prominent cold component ascribed to an earlier stage of
evolution than Group II. Disk evolution can be constrained from the comparison
of disks with different properties. A first attempt of disk taxonomy is now
possible thanks to the increasing number of high-resolution images of Herbig
Ae/Be stars becoming available. Near-IR images of six Group II disks in
scattered light were obtained with VLT/NACO in Polarimetric Differential
Imaging, which is the most efficient technique to image the light scattered by
the disk material close to the stars. We compare the stellar/disk properties of
this sample with those of well-studied Group I sources available from the
literature. Three Group II disks are detected. The brightness distribution in
the disk of HD163296 indicates the presence of a persistent ring-like structure
with a possible connection with the CO snowline. A rather compact (less than
100 AU) disk is detected around HD142666 and AK Sco. A taxonomic analysis of 17
Herbig Ae/Be sources reveals that the difference between Group I and Group II
is due to the presence or absence of a large disk cavity (larger than 5 AU).
There is no evidence supporting the evolution from Group I to Group II. Group
II are not evolved version of the Group I. Within the Group II disks, very
different geometries (both self-shadowed and compact) exist. HD163296 could be
the primordial version of a typical Group I. Other Group II, like AK Sco and
HD142666, could be smaller counterpart of Group I unable to open cavities as
large as those of Group I.Comment: 16 pages, 7 figures, published by A&
Observations of gas flows inside a protoplanetary gap
Gaseous giant planet formation is thought to occur in the first few million
years following stellar birth. Models predict that giant planet formation
carves a deep gap in the dust component (shallower in the gas). Infrared
observations of the disk around the young star HD142527, at ~140pc, found an
inner disk ~10AU in radius, surrounded by a particularly large gap, with a
disrupted outer disk beyond 140AU, indicative of a perturbing planetary-mass
body at ~90 AU. From radio observations, the bulk mass is molecular and lies in
the outer disk, whose continuum emission has a horseshoe morphology. The
vigorous stellar accretion rate would deplete the inner disk in less than a
year, so in order to sustain the observed accretion, matter must flow from the
outer-disk into the cavity and cross the gap. In dynamical models, the putative
protoplanets channel outer-disk material into gap-crossing bridges that feed
stellar accretion through the inner disk. Here we report observations with the
Atacama Large Millimetre Array (ALMA) that reveal diffuse CO gas inside the
gap, with denser HCO+ gas along gap-crossing filaments, and that confirm the
horseshoe morphology of the outer disk. The estimated flow rate of the gas is
in the range 7E-9 to 2E-7 Msun/yr, which is sufficient to maintain accretion
onto the star at the present rate
NaCo polarimetric observations of Sz 91 transitional disc: a remarkable case of dust filtering
We present polarized light observations of the transitional disc around Sz 91 acquired with
VLT/NaCo at H (1.7μm) and Ks (2.2μm) bands. We resolve the disc and detect polarized
emission up to ∼0.5 arcsec (∼80 au) along with a central cavity at both bands. We computed a
radiative transfer model that accounts for the main characteristics of the polarized observations.
We found that the emission is best explained by small, porous grains distributed in a disc with
a ∼45 au cavity. Previous ALMA observations have revealed a large sub-mm cavity (∼83
au) and extended gas emission from the innermost (<16 au) regions up to almost 400 au
from the star. Dynamical clearing by multiple low-mass planets arises as the most probable
mechanism for the origin of Sz 91’s peculiar structure. Using new L
-
band ADI observations,
we can rule out companions more massive than Mp ≥ 8 MJup beyond 45 au assuming hot-start
models. The disc is clearly asymmetric in polarized light along the minor axis, with the north
side brighter than the south side. Differences in position angle between the disc observed at
sub-mm wavelengths with ALMA and our NaCo observations were found. This suggests that
the disc around Sz 91 could be highly structured. Higher signal-to-noise near-IR and sub-mm
observations are needed to confirm the existence of such structures and to improve the current
understanding of the origin of transitional discs.Indexación: Scopu
Imaging the water snow-line during a protostellar outburst
A snow-line is the region of a protoplanetary disk at which a major volatile, such as water or carbon monoxide, reaches its condensation temperature. Snow-lines play a crucial role in disk evolution by promoting the rapid growth of ice-covered grains^1, 2, 3, 4, 5, 6. Signatures of the carbon monoxide snow-line (at temperatures of around 20 kelvin) have recently been imaged in the disks surrounding the pre-main-sequence stars TW Hydra^7, 8, 9 and HD163296 (refs 3, 10), at distances of about 30 astronomical units (au) from the star. But the water snow-line of a protoplanetary disk (at temperatures of more than 100 kelvin) has not hitherto been seen, as it generally lies very close to the star (less than 5 au away for solar-type stars^11). Water-ice is important because it regulates the efficiency of dust and planetesimal coagulation5, and the formation of comets, ice giants and the cores of gas giants^12. Here we report images at 0.03-arcsec resolution (12 au) of the protoplanetary disk around V883 Ori, a protostar of 1.3 solar masses that is undergoing an outburst in luminosity arising from a temporary increase in the accretion rate^13. We find an intensity break corresponding to an abrupt change in the optical depth at about 42 au, where the elevated disk temperature approaches the condensation point of water, from which we conclude that the outburst has moved the water snow-line. The spectral behaviour across the snow-line confirms recent model predictions^14: dust fragmentation and the inhibition of grain growth at higher temperatures results in soaring grain number densities and optical depths. As most planetary systems are expected to experience outbursts caused by accretion during their formation^15, 16, our results imply that highly dynamical water snow-lines must be considered when developing models of disk evolution and planet formation
Sparse aperture masking observations of the FL Cha pre-transitional disk
We present deep Sparse Aperture Masking (SAM) observations obtained with the ESO Very Large Telescope of the pre-transitional disk object FL Cha (SpT = K8, d = 160 pc), the disk of which is known to have a wide optically thin gap separating optically thick inner and outer disk components. We find non-zero closure phases, indicating a significant flux asymmetry in the KS -band emission (e.g., a departure from a single point source detection). We also present radiative transfer modeling of the spectral energy distribution of the FL Cha system and find that the gap extends from 0.06+0.05- 0.01 AU to 8.3 ± 1.3 AU. We demonstrate that the non-zero closure phases can be explained almost equally well by starlight scattered off the inner edge of the outer disk or by a (sub)stellar companion. Single-epoch, single-wavelength SAM observations of transitional disks with large cavities that could become resolved should thus be interpreted with caution, taking the disk and its properties into consideration. In the context of a binary model, the signal is most consistent with a high-contrast (ΔKS ∼ 4.8 mag) source at a ∼40 mas (6 AU) projected separation. However, the flux ratio and separation parameters remain highly degenerate and a much brighter source (ΔKS ∼ 1 mag) at 15 mas (2.4 AU) can also reproduce the signal. Second-epoch, multi-wavelength observations are needed to establish the nature of the SAM detection in FL Cha